1. Field of the Invention
The invention relates to the field of magnetic media data storage devices and more particularly, to methods of detecting misalignment of movable read-write transducer heads with respect to magnetic media. Magnetic media data storage devices have data arranged on the magnetic media in tracks, and a read-write transducer head is movable across the media such that it can be aligned with any of the data tracks on the media. The head must be accurately aligned with the desired data track for effective transfer of data. The more closely the tracks are spaced together, the more data can be stored on a given sized media, but the more critical the alignment of the head becomes. A typical application of the present invention is on a data storage utilizing a magnetic disk as the data storage media. A disk is a plotter-like element having magnetic material coated or plated on, or incorporated in, one or both surfaces of said element and primarily designed for magnetically storing digital information by recording while said element is rotating. Magnetic-disk data storage devices are made with a great variety of size and sophistication. Constantly competing design criteria involve attempting to increase performance while attempting to decrease cost. One of the significant factors controlling the characteristics of various data storage devices currently available is how the particular designer balanced those particular competing criteria. In the large, high density storage devices, some fairly elaborate systems of controlling head alignment can be justified. In the lower priced devices, not much can be spent controlling precision alignment.
2. Description of the Prior Art
A fairly elaborate system of control of head alignment is described by Chick, et al in U.S. Pat. No. 4,136,365. Chick discloses a system utilizing a special disk with built-in reference tracks, and provides for an intermittent process of checking the alignment of the head with respect to the reference tracks on the disk, and then making adjustments to compensate for any alignment error.
While a system which requires a special disk and which automatically compensates for misalignment can be justified on large high density storage devices, the tendency with regard to the lower priced, less sophisticated devices is to simply have the alignment routinely checked at the time of servicing through a manual alignment process. A disadvantage of having alignment checked only when the device is serviced, is that if alignment drifts, not only may it be an undetected cause of data reading errors, but data recorded on a disk while the head is out of alignment may be lost when the head alignment is corrected.